Provided is an unique, efficient and cost-effective process for the recovery of acid from acid-rich solutions. The process of the subject matter utilizes a strong oxidizer, such as Caro's acid, to disintegrate or render insoluble organic or inorganic materials such as carbohydrates and complexes thereof contained in acid-rich solutions, to make efficient and simple the separation and recovery of the acid solution. The acid recovered thus obtained is free of organic matter, and containing nearly all of the acid originally contained in the acid-rich solution.

Provided is a method for treating sulfuric acid comprising the step (I) of bringing said sulfuric acid into contact with a collection of solid particles (B) having BET surface area of 50 m.sup.2/g to 5,000 m.sup.2/g and having volume-average particle diameter of 200 m or less.

Acid hydrolysis of biomass is an important step for releasing the component sugars before converting them to fuels and/or biochemicals. During such a process, a significant amount of mineral acid, such as sulfuric acid, is used. In most cases, the residual acid is neutralized with lime before the sugar conversion step. By doing so, a waste calcium sulphate stream is generated and sent to disposal. The efficient separation of acid from the sugars would allow the recycle of the acid and make the entire process more economically viable. We found that a resin bed packed with an acid retardation resin can be used to achieve an efficient separation (i.e. 98.5% recovery of the acid) of the sulfuric acid from the sugars. The resin bed can be simply regenerated with water.

Provided is a method for reacting a resin with sulfuric acid comprising the step of heating a reaction mixture to a temperature of 80 C. or higher, wherein said reaction mixture comprises (a) a collection of copolymer particles (A), (b) sulfuric acid, and (c) a collection of solid particles (B) different from said copolymer particles (A), wherein said solid particles (B) have BET surface area of 50 m.sup.2/g to 5,000 m.sup.2/g.

Provided is a method for treating sulfuric acid comprising the step (I) of bringing said sulfuric acid into contact with a collection of solid particles (B) having BET surface area of 50 m.sup.2/g to 5,000 m.sup.2/g and having volume-average particle diameter of 200 m or less.